Apparatus for aircraft control in accordance with attack angle



ACCORDANCE WITH ATTACK ANGLE Filed Dec.

INVENTOR. WALDO H. KUEVER ATTORNEY May 4, 1954 125 6528 .l 565 @2525 F5225; mwl 1 3 8 mzzo x0555 Gzzfifi 559:: N: I s 1 w 5 3 1 E: l mm. N2 & mz ozwzwm f h] mwwwm M322 V652 09 m. 5.59.: 5 my 53 Patented May 4, 1954- APPARATUS FOR AIRCRAFT CONTROL IN ACCORDANCE WITH ATTACK ANGLE Waldo H. Kliever, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application December 35), 1948, Serial No. 68,237

.24 Claims.

This invention relates to the field of aircraft control apparatus, and more particularly to'such apparatus as is designed to bring about and maintain a selected condition of flight of the craft.

Various characteristics of craft operation have been-made use of from time to time :as measures of preferred operation of the craft. Characteristics so used in the past include attitude, air speed, altitude, power output, etc, and one or more of the controlling members of the craft,

such as elevators, ailerons, throttles, etc, have been-controlled in the various systems.

The present invention has for a broad object to provide improved apparatus for controlling the performance of :a craft in accordance with angle of attack.

It is also an object of the invention to provide an apparatus of the above type with automatic overriding means'bec'oming efiective as the angle of attack exceeds 'a selected value.

It is another object of the invention to provide such apparatus in which the performance of a craft is controlled in accordance with attack angle by simultaneously altering the throttle and elevator settings.

It is another object of the invention to provide apparatus in which flight of the craft can be maintained at an adjustable angle of attack, by means of control exerted by an attack angle sensing unit over the elevators and throttles oi the craft.

It is another object of the invention to provide apparatus of the type described in which the ratio between the control exerted by the attack angle sensing unit over the elevators oi the craft and the control exerted over the throttles oi the craft may be varied.

A further object of the invention to provide 'ilight contml apparatus for maintaining a constant angle of attack in an attitude-stabilized craft, by simultaneously coi'itrollin the elevators and throttle of the craft.

It is a further object of the invention to provide flight control apparatus effective when the angleof attack exceeds a selected value to cause corrective operation of both the elevators and the throttle.

It is a further object of the invention to provide flight control apparatus for causing a craft to follow a radio glide path at a constant angle of attack.

A still further object of the invention is to provide app a ms of the type just described in which ck angle sensing device performs the desired function by simultaneously contrclling the throttles and elevators of the craft.

Yet another object of t .e invention is to provide apparatus of the type just described in which the attitude of the craft is stabilized at 2 all times independently of the attack angle control.

Various other objects, advantages, and features of novelty which characterize my invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects attained by its use, reference should. behad to the subjoined drawing, which forms a further part hereof, and to the accompanying descriptive matter, in which I have illustrated and described a preferred embodiment of my invention.

The single figure 'of the drawing schematically illustrates aircraft control apparatus according to the invention.

It is well known to those skilled in aerodynamics that the movement of a craft in flight, in a vertical plane through the longitudinal axis of the craft, is controlled in an interrelated fashion by the elevators and throttles of the --cra-f-t, which govern its attitude, its air speed, and its rate of climb or glide. Controlsystems are known for regulating each of these characteristics, to give night at a constantaltitude, a'constant air speed, or a constant attitude. It is also known to construct systems in which more than one of these characteristics is controlled, such for example as air speed and altitude. Heretofore, howevensuch systems have also'included sensing means responding to the several characteristics to be controlled.

The attack angle of a craft, while a single characteristic, is related to air speed, attitude, and change in altitude. Moreover, attack angle is very closely related to tendency of a craft to stall, which can take place at any air speed or at any attitude. Control of a craft in accordance with attack angle is thus very advantageous both because of the fundamental nature of the variable being sensed in its relation toother more restricted variables, and because of the direct relation between the attack angle and stall.

The latter feature cannot be overemphasized. Stall is not simply a nose-high, low-speed, lowpower phenomenon. It is possible to stall at full throttle, or at high speed,'or in'a diving attitude: stalling in power dives was found to be a source of considerable danger until this principle was accepted. Moreover, in modern craft designed for high wing loading it is very :difiicult for "the human pilot to make an accurate estimate of his angle of attack. Because of this uncertainty, the pilot must operate the craft so as to be sure of a small enough angle of attack for safety: as a result landing speeds are higher than necessary requiring longer runways. A second result of the uncerdainty as to the exact attack angle is reduced operating range, since only for a particular attack angle is the craft most efiicient.

The importance of attack angle has not been overlooked entirely: numerous proposals have been made particularly for indicators to warn the pilot if his attack angle is becoming so large that a stall is imminent. The use of attack angle as a variable in response to which a craft is to be controlled, by means of the elevators and throttles of the craft, has not heretofore been suggested; however, a system of control along these lines is described herein.

As shown in the figure, the system is to be installed in an aircraft having pitch control surface means It, comprising the elevators of the craft, and power control means II, comprising the throttles of the craft. For the sake of simplicity in illustration the craft is illustrated as having only a single engine. The system is also shown as comprising the air-borne components I2 of an instrument landing system, for causing the craft to follow a selected glide path, and a vertical gyroscope I3 for establishing a standard of attitude with respect to the earth. Th elevators are normally actuated by a control stick I4, and a throttle lever 55 is arranged for actuating the throttle II, the throttle position comprising a factor afiecting engine operation. In the practice of the invention the throttle setting is adjusted by a throttle servomotor I5 energized from a throttle amplifier II, and the elevators are controlled by an elevator servomotor 29 energized from an elevator amplifier 2| whose input includes an elevator bridge 22, which may comprise portions of a more elaborate automatic pilot.

The system further includes an attack angle control unit 24 having a throttle channel 25 and elevator channel 26, both influenced by a mechanical input 21 from an attack angle sensing unit 30, which also drives an indicator 29 either directly or through a suitable telemetric system. The various general components enumerated above will now be considered in further detail.

The system is energized with alternating voltage from a plurality of transformer secondary windings. In the drawing these windings are shown as provided with individual cores and primary windings, but it will of course be realized that it is equally satisfactory to provide a single primary winding for all the secondary windings.

The elevator bridge 22 is energized from the secondary winding 3! of a transformer 32 having a primary winding 33. Bridge 22 comprises the parallel connection of the windings 34 and 35 of a pair of voltage dividers 36 and 37 having sliders 49 and 4I all respectively.

Sliders 40 and 4! comprise the output terminals of the bridge; slider 40 is moved with respect to winding 34 by mechanical connection 42 to vertical gyroscope I3, so that its position with respect to winding 34 changes as the craft changes its pitch attitude. Gyroscope I3 is pro vided with a second output 43 for use in connection with the roll axis of the craft.

Slider 4| of bridge 22 is actuated by a mechanical connection M to elevator servomotor 20. This servomotor is energized through a suitable multi-conductor cable 65 from amplifier H, which has power terminals 49 and 41 energized from. the source of alternating voltage, and input terminals as and 5|, the latter being grounded as at 52. Terminal 50 is connected to slider 4! of bridge 22.

Mechanical connection 44 is continued so that motor 20 may actuate elevators I0, control stick I4 moving in accordancewith the operation of motor 20 and the elevators. A suitable disconnect may be provided between control stick I4 and servomotor 20 if desired, so that emergency op eration of the elevator may be carried on by the control stick regardless of the servomotor.

Servomotor 20 is preferably provided with a clutch which is energized electrically, to interconnect shaft 44 with the motor, when the latter is energized from amplifier 2|. The motoramplifier combination is of the well known type in which th motor is energized for forward or reverse operation according to the phase of a reversible signal supplied to the amplifier and in which the motor does not move in either direction when the amplifier has no signal voltage. This also applies to motor I6 and amplifier I'I.

Instrument landing system I2 may be of any suitable type which provides a mechanical output 54 whose sense and magnitude depend upon the amount and direction of displacement of the craft from a desired landing path. Such instruments are known in the art, one suitable form thereof being disclosed in copending application 49,442 of Alderson and Carpenter filed September 15, 1948 and assigned to the assignee of the present application. By means of mechanical connection 54, th instrument landing system [2 actuates the slider 56 of a voltage divider 51 having a winding 60 which is center tapped at 6|. Winding 60 is energized from the secondary winding 32 of a transformer 63 having a primary winding 64 energized from the source of alternating voltage. Slider 55 is connected by conductor 65 to slider 40 of bridge 22.

Vane 30 acts through mechanical connection 2'! to actuate the slider 66 of a voltage divider 61 with respect to its winding ID. This winding is metallized as at H over the major portion of its length, so that for any position of vane 35! within this wide range the metallized portion II acts as a short circuit between slider 66 and terminal I2 of the winding. Terminal I2 is connected by conductor I3 to center tap SI of voltage divider 57. Winding ID of voltage divider 6! is energized from the secondary winding 14 of a transformer I5 having a primary winding I6 energized from the source of alternating voltage. The purpose of this structure will be more fully explained below.

Transformer I5 and voltage divider 6! comprise the stall prevention portion of elevator channel 26, which also includes a control surface bridge II energized from the secondary winding of a transformer 8| having a primary winding 82 energized from the source of alternating voltage. The bridge comprises the windings 83 and 84 of a pair of voltage dividers 85 and 85 having sliders 81 and respectively. Slider 90 is grounded at 9!. The winding 92 of a voltage divider 93 having a slider 94 is connected between sliders 8'! and 90 of bridge 11 by means of conductors 95 and 95.

Sliders 8'! and 90 are the output terminals of bridge 11, and of the voltage appearing between the output terminals a portion determined by the position of slider 94 appears between the slider and ground. Slider 94 is connected to slider 65 of voltage divider ET by conductor 98. Slider ST is actuated by mechanical connection 2! from attack angle sensing vane 30. Slider St is actuated by a mechanical connection 91 to a man ually operated selector knob I00 whose pointer moves with respect to a scale 99. Slider 94 is actuated by a mechanical connection IUI to amanually operated knob I02.

The input circuit to amplifier 2| may now be traced from terminal 5| through ground connec tions 5-2 and 9 I, conductorSG, the portion-of winding 92 below slider 94, the slider, conductor 98, slider 66., the portion of winding 10 to the right of slider 66, terminal 12, conductor 13,:center tap SI, the portion of winding 6|] between :center tap "6| and slider 56, the slider, conductor 65, slider 40, bridge 22, slider '41, and conductor 53 to input terminal 56 of the amplifier. This input circuit accordingly comprises the series addition of four voltages, a portion of the output from bridge 11 as determined by the position of slider 94, the output of the elevator stallcpreventioncircuit, the

output of voltage divider 51, and the output of bridge 22. When these voltages add up to zero, amplifier 2! is deenergized and elevator servomotor does not operate. When the voltages do not add up to zero, amplifier 2=I energized with alternating voltage of a first phase or of I the'opposite phase, and servomotor 2B is energized for operation in one sense or the othenadjusting the position of elevator I8 and alsomoving slider 4| with respect to winding 35 to reduce the magnitude of the input to the amplifier.

Throttle channel of :attack angle control unit 24 is constructed in the same fashion as elevator channel A throttle bridge "I Ii! is energized from the secondarywinding II I of a transformer -I-I-2 having a primary Winding -I'I3 con-- nected to the source of alternating voltage. The voltage supplied by secondary winding 'I H is conveniently equal to that supplied by secondary winding 80. Bridge I I0 comprises the windings I I4 and II 5 of apairof voltage dividers H6 and i ll having sliders i251 and HI. Slider 112i is grounded at I28. The winding 124 of a voltage divider having a slider 12% is connected between sliders I26 and HI of bridge III by means of conductors I22 and I23. Sliders I20 and I2I are the output terminals of bridge 11 0.,aand of the voltage appearing between these output termina-ls a portion determined by the position of slider I 26 appears between the slider :and ground.

Slider I2!) is actuated by mechanical-connection 27 from sensing vane 36. Slider 126 is actuated by mechanical connection I03 to a manually -operable knob I64. Slider IN is actuated by me chanical connection -91 to selector knob I00, the

connection being such that sliders IZI and 90 move in the same direction along their windings when knob I00 is turned.

Slider it-6 is connected by a conductor I-21 to one terminal I31 of a voltage divider I-3I having a slider use and a winding I32, a major portion of which is metallized as at I33, as described in connection with winding 1c. Winding l3'2is-energized from the secondarywinding I734 of .a trans former I35 having a primary winding I36 energized from the source of alternating voltage.

Slider I50 is connected by a conductor Mil to a center tap MI on the winding I42 of a voltage divider M3 having a slider I44. Winding 1-4-2 is energized from the secondary winding I45 of a transformer Mt; having a primary winding M1 energized from the source of alternating voltage.

Slider I4 is connected by a conductor I to the slider I51 of a voltage divider :I52 having a winding 153 center tapped at I54. Winding I53 may be either linear, or characterized according to the relation between attack angle and throttle setting, and is energized from the secondary winding I55 of a transformer I56 having :a primary winding 4 .5.1 energized from the :source "of alternating voltage.

Slider I'M is actuated :bymechanical connection from instrument landingsystem I2. Slider .I'5I

is actuated simultaneously with operation of throttle II :from servomotor I6 by means of a mechanical connection I60 including a manual override 16! which provides means whereby throttle II can be actuated by manual lever I5 regardless :of the operation of servomotor I6: when the throttle is adjusted by motor I6, the manual lever is also moved.

Motor I 6 is energized through a multi-conductor cable I52 from amplifier 11, which has power terminals 563 and 164, energized from the source of alternating voltage, and input terminals I and IE6, the latter being grounded at I61. Input terminal IE5 is connected to center tap 154 by conductor I 16.

The input circuit to amplifier I1 may be traced from input terminal res through ground connections l61 and I28, 0 inductor i262, the portion of winding I24 below slider I26, the slider, conductor I21, terminal I31, the portion of winding I32 between the terminal and slider 13.0, the slider, conductor I46, center tap Hit, the portion of winding I42 betweenthe center tap and'slider M4, the slider, conductor !56, slider I51, the port'ion'oi winding I 53 between'the slider and center tap I54, the center tap, and conductor Hi) to input terminal I65. It :is thus evident that the input to the amplifier comprises a series connection of four voltages, aportion of the output vol age of bridge H0 "as determined :by the position of slider I26, the output from the throttle stall prevention circuit, the output of voltage divider I43, and that from voltage divider I53. So long as the comet these voltages is zero, the amplifier unenergized, and .opcration cf motor t6 does not take place. Whenever the sum of the voltages is notzero, the amplifieris energized accordingly,

and motor I 6 operates in one sense or the other, adjusting the position of throttle !I and also moving slider I'5I with respect to winding I53 to reduce the magnitude of the'input to the ampliher.

In installing the system, mechanical. connection i659 is adjusted so that "movement of slider I5I from one end to the other of winding W3 accompanies movement of throttle I I through a se lected range which may be the full extent of its possible movement. lviechanieal connection 54 is so adjusted that sliders 56 and it; are at center taps 6| and MI respectively when the craft is exactly on the desired. instrument landing beam and so that departure of the craft from the de sired-beam in either direction to a selected extent results in movement of the sliders in either direc tion to the ends of their windings. It may also he preferred to put taps 6! and MI at points other than the centers of their respective windings. The instrument landing system is normally deencrgized with sliders I'M and "55 engaging center taps It! and 6! respectively.

li le'chan-ical connection 44 is adjusted so that slider moves from one end of winding 35 to the other for a selected range of movement of elevators i t, and so that'the slider is at the center of winding when the elevators are streamlined. Winding '34 carried by the craft, and slider it is stabilized hy gyroscope I3. Mechaniconnecticn 42 is so adjusted that when the craft'is in'a normal attitude about its pitch axis, the center of winding .34 comes into alignment with slider 4. and so that the range-of relative movement of slider 48 and winding 34 'corresponds to adesired range of attitude change.

Mechanical connection 27 is so adjusted that sliders 66, 81, 20, and I30, which move unitarily, are at the right hand ends of their windings when the attack angle as sensed by Vane 30 is 12, and at the left hand ends of their windings when the angle is +18. The meta-llized portions of windings l and I30 extend from the right hand ends of the windings to the positions assumed by sliders 58 and 130 when the attack angle has some arbitrary value, as +12": this angle is selected with special reference to the aerodynamic characteristics of each craft being equipped, and represents the maximum safe attack angle for that craft. The stalling angle is naturally slightly greater.

The initial adjustment of the system must now be made. For his purpose sliders 90 and HI are temporarily disconnected from shaft 9?, so that they be independently adjusted along their respective windings, slider I! is temporarily disconnected from shaft I60 and set to the position in which it engages center tap I5l, and motors I6 and 2B are temporarily disconnected from shafts 44 and. E60. Sliders 94 and I25 are set at the centers of their windings, and the electical system is energized. The craft is brought into a condition of flight in smooth air at a constant altitude and a normal cruising speed by manual operation of throttle lever I5 and control stick i 4: under these conditions the craft is in the normal attitude at the normal attack angle of say 4, with the elevators streamlined. Vane 39 adjusts sliders I30, I20, 81 and 8'6 in accordance with the value of the normal attack angle: sliders 90 and IZI are then separately adjusted by hand until motors I5 and are deenergized simultaneously. Knob I00 is next set at 4 on scale 99, sliders 9i and I2l are reconnected to shaft 9?, slider SI and motor I 6 are reconnected to shaft 69, and motor 20 is reconnected to shaft 44. The apparatus is now in control of the craft, and operates to maintain its attack angle constant at the value for which the system was adjusted.

Knob IE0 is now moved to a new reading on scale 99 displacing sliders 90 and I2I: when op eration of motors I6 and 20 again ceases the rate of climb of the craft is observed on an auxiliary rate of climb meter, and knobs I02 and I03 are operated until constant altitude flight is achieved at the new selected angle of attack. Change in altitude is corrected by moving slider 94 along winding 92 and any ensuing departure from the selected angle of attack is corrected by adjustment of the position of slider I26. Since power and attitude are interrelated, it may be necessary to repeat these adjustments until the desired condition is achieved. The system is now ready for use.

Operation In explaining the operation of this system it will at first be assumed that the craft has manually been brought into the condition of normal cruising flight just described, the instrument landing system being deenergized with sliders 55 and M4 at their center taps, and sliders 94 and I being at the centers of their respective windings. Slider I5I is at some particular position on winding E53, by reason of manual adjustment of lever i5, slider 41 is at the center of winding because the elevators are streamlined, and slider 43 is at the center of winding 34 because the craft is in the normal attitude. Vane 30 is in a position determined by the actual attack angle of the craft, which may for example be +4", and sliders 66, 8'1, I20 and I30 are set in accordance with the position of vane 30 by connection 21.

When the system is electrically energized, there are impressed on the input to amplifier 2 I the sum of the four voltages previously listed. One of these is the output of bridge 22, which is zero since slider and 4I are both at the centers of their windings-the craft being in the normal attitude and the elevators being streamlined.

Two others of the voltages which add to comprise the input to amplifier 24 are of zero magnitude, because slider is at center tap GI, and slider is on metallized section ll of winding 10. The fourth voltage is the output of bridge 11, which must also be zero since the voltage on amplifier 2I is zero. Slider B! is set at a position proportional to 4 by vane 30, and this determines the position of slider 90, which must be displaced from center of winding 84 in the same direction and to the same extent as slider 87.

Under the same conditions the sum of four voltages is also impressed on the input to amplifier I'l. Of these, the voltage between terminal I37 and slider I30, the voltage between center tap MI and slider I 44, and the voltage between center tap I54 and slider I5I are of zero magnitude, and that from bridge IIO, like that from bridge T7, is also zero.

So long as the flight of the craft continues at the attack angle of 4, no input is supplied to amplifiers I! and 2|. Change in the attack angle of the craft due for example to change in the position of its center of gravity, decreases in load due to fuel consumption, vertical components of air movement, etc.causes movement of vane 30 and hence of sliders 8'! and I20. If the attack angle becomes 5", for example, bridges IT and III) are no longer balanced, and amplifiers I? and 2I are energized.

Motor IB operates in a direction to increase the power supplied by throttle II, and motor 20 operates in a direction to give down elevator. Simultaneously slider I5I is moved to a position in which the unbalance voltag from bridge IIB is neutralized by an equal voltage of opposite phase from voltage divider I52, and slider M is moved to a position in which the unbalance voltage from bridge I1 is neutralized by an equal unbalance voltage of opposite phase from bridge 22.

A a result of adjustment of the throttles and elevators the craft noses down and its air speed increases. These changes alter the value of the attack angle acting on vane 30, and sliders I20 and 8'! are moved in a direction to decrease the unbalance voltages of bridges H0 and ll. The change in attitude of the craft also results in displacement of windin 34 with respect to slider 4U. which reduces the unbalance of bridge 22. These efiects combine to cause reverse energization of amplifiers I I and 2I, and reverse operation of motors I6 and 20 results, partially returning throttle II and elevators I0 to their original positions. If the condition which caused the angle of attack to change was a temporary one, the attitude and power of the craft continue to change causing continued movement of elevators I 0 and throttle I I back to their original positions when the attack angle again assume the desired value. If, on the other hand, the condition which caused the attack angle to change is a permanent one, such as a permanent shift in the loading of the plane, a condition of equilibrium is reached in which the bridges l1 and H0 are slightly unbalanced to maintain the elevators it and the throttle It in new: positions. Whileunder these conditions: the attack angle is not restored exactly to its original value; nevertheless. bya proper selection of the voltages applied to the bridges, the departure of the attack anglefrom the selected desired value canbemade to be relatively small;

If it. is desired to doso, change in the attackangle for the craft may be brought about simply by setting the index of knob lift to the proper point on the scale. The desired attach angle may be that corresponding togreatest engine efficiency, or to maximum cruisin range, or to minimum safe landing speed; according tothe desires oftheoperator.

In thelatt-er example the-craft is coming into an area whereturbulent airandverti'cal currents may be expected, and are. especially dangerous, Changes in the configuration of: the craft, such as lowering of: wing flaps and landing gear, also take place at this time. For minimum landingspeed, there must bee-maximum attack a-ngl'e short of thatresulting-in stall conditions. In landings controlled by human pilots the actual maximum cannot be determined accurately and: a margin for safety mustbeallowed According" to the present invention, on the other hand',the attacl: angle is known atallti'mes; so that the safe maximum: value thereof may be set intothesystem and used? to control the craft.

If, due to the conditions. of landing, the attack angle increases beyond this:- selected safe value, not only dooridges: 1: I 0 and? l energize" amplifiersli. and 21, to cause operation of motors it and 26 to decrease the attack angle, but voltages are independently supplied in the elevator and throttle channels: from sliders 6t and lilii, which are moved off the metallized portions of their windings. when the safe angle is exceeded; These latter voltages persist until a safe value of attack angle is restored; regardless of the condition of bridges 1-1 and Hliar a: valuable safety feature isthusincorporated into the inventive system.

Whenthe. craft is preparin toland', instrument landing system I12: is energized and in thecourse of itsoperationsliderstfi: and i441 are moved with respect: to. their windings. An inspection of the drawing makes: it: clear that the throttle channel: of. the; controlsystem is altered by the addition of the; voltage appearing between slider 144' andcenter tap lfislr. similarly, the elevator chan--- nel of the system is altered by the addition of the voltage between slider 58? and center tap 61. So long, as the craft-is on the proper-glide path, sliders 56 and M4 remain v at the center taps of theirrespective windings butif'the craft moves off the proper glide path, sliders I44 and 56 are movedto supply voltages-in both channel'sof the system. of sucha nature as to cause operation of the elevators and throttles to. return the craft to the-desiredglidepath.

The senseof the: voltages supplied-by operation of. member. 5.4 is. critical. It the. craft is above the beam. the voltage supplied by: divider M3 is of. a phase to. reduce; the power by closing the throttle, and the voltagelsupplied by divider 51': is: of a phase to give down elevator. By this relation it; is possible: to; cause the craft to lose atti tude; while. maintaining. the desired attach angle.

It will be appreciated that if the selected-attack angle, is very: close tothe maximum safe value, the; presence of a. large signal? in either channel dueto operation of" the instrument landing system could very: easily bring the: craft into a stalling condition. by reason of increasing the 10 attack angle beyond that called: forby' bridges ll and [10. In this connection the stall preventionvoltages from' voltage dividers l3il and: G1 are especially valuable.

In the foregoing disclosure I haved'escribed an aircraft control system in Whichtheattack angleof' the craft isusedto control the throttles and elevators of the craft in a desired ratio, together with means continuously ready to cause-corrective operation; of these control members if the attack angle exceeds a safe value no matter what the selected attack angle may be. Obviously a constant attitude control could besubstituted for the instrument landing system 50, if desired.

Numerous objects and advantagesof my invention have been set forthin theforegoing description, together with details of the structure and function of the invention, and the novel features thereofare pointed out in the appended claims. The disclosure, however, is illustrative only, and I may make-changes in detail, especially in matters of shape, size andarrangement of parts, within the principle of the invention, to thefull extent indicated by the broad general meaning of;

-- the terms. in which the appended claims are expressed.

I claim as my invention:

1. In apparatus of the class described, in combination: a: control surface; a motor drive for said control surface; an attack angle selecting device, an attack angle responsive device; a halanceable system including .a portion adjusted by said selecting deviceancl' a portion adjusted by said responsive device; said system being inbalance when the actual attack angle isthat selected; and means effective upon unbalance of said systemto energize said motor for adjusting said control surface:

2r. In apparatus of thecl'ass described, in combinatiorr: a contror surface; a motor drivefor said control surface; a balanceable system including means responsive solely to actualattack angle'and-an' attack angle selecting device; said system being in balance when the actualattack angle is that selected; means effective upon unbalance of said system to energize said motorfor adjusting said" control surface; and further means for causing operation of said motor in a direction resulting in decrease in the attack angle-whenever it exceedsa predetermined value.

3. In apparatus of theclass-described, in combinati'oirza throttle; a motor drive for said throttle; a control surface; a motor driveforsaidr control surface; a balanceable system includingmeans responsive solely to actual attack angle and an attack: angle selecting device, said system being in baiancewhen the actual attack angleisthat selected; means effective upon unbalance of said system" to energize-said motors for adjusting said throttle and said control surface; and fur-- thei means for causing energization of at least one of said motor means foroperati'ontoreduce said attack anglewhenever said attack angle exceeds a predetermined value.

4-. In apparatus of the class described; incombination: a throttle; a motordrive' for said throttle; a control surface; a motor drive for said control surface; a bal'anceablesystem including means responsive solely to actual attack angle and ail-attackanglesel'ecting device, said system beingin balance when the actual attack angle is that selected; means effectiveupon unbalanceof said system to energize said motors for adjustingsaid throttle and said control surface; and

further means for causing energization of said motor means for operation to reduce said attack angle whenever said attack angle exceeds a predetermined value.

5. In apparatus of the class described, in combination: a control surface; a motor drive for said control surface; a vertical gyroscope; means responsive solely to actual attack angle; an attack angle selecting device; a balanceable system including means adjustable by said attack angle responsive means, said attack angle selective device, said vertical gyroscope, and said control surface, said system being in balance w ien the actual attack angle is that selected and when said craft is in a pitch attitude determined by said vertical gyroscope; and means effective upon unbalance of said system to energize said motor for adjusting said control surface.

6. In apparatus of the class described, in combination: a. control surface; a motor drive for said control surface; a vertical gyroscope; means responsive solely to actual attack angle; an attack angle selecting device; a balanceable system including means adjustable by said attack angle responsive device, said attack angle selecting device, said vertical gyroscope, and said control surface, said system being in balance when the actual attack angle is that selected and when said craft is in a pitch attitude determined by said vertical gyroscope: means effective upon I unbalance of said system to energize said motor for adjusting said control surface; and further means for causing energization of said motor to decrease said attack angle whenever said angle exceeds a predetermined value.

7. In apparatus of the class described, in combination: a throttle; a motor drive for said throttle; a control surface; a motor drive for said control surface; an instrument landing system responsive to departure of an aircraft from a predetermined glide path; means responsive solely to actual attack angle; an attack angle selecting device; a balanceable system including means actuated by said responsive device, said selecting device, and said instrument landing system, said balanceable system being in balance when the attack angle is that selected, and when the craft is located on an instrument landing path; and means effective upon unbalance of said system to energize said motors for adjusting said throttle and said control surface.

8. In apparatus of the class described, in combination: a control surface; a motor drive for said control surface; means responsive solely to actual attack angle; an attack angle selecting device; a vertical gyroscope; an instrument landing system responsive to departure of an aircraft from a predetermined glide path; a balanceable system including means actuated from said responsive device, said selecting device, said gyroscope, and said instrument landing system, said balanceable system being in balance when the attack angle is that selected, and when the craft is located on an instrument landing path; and means effective upon unbalance of said system to energize said motor for adjusting said elevators to return said system to a balanced condition.

9. In apparatus of the class described, in combination: a throttle; a motor drive for said throttle; a control surface; a motor drive for said control surface; means responsive solely to actual attack angle; an attack angle selecting device; a vertical gyroscope; an instrument landing system responsive to departure of an aircraft from a predetermined glide path; a balanceable system including means actuated from said attack angle responsive device, said selecting device, said gyroscope, and said instrument landing system, said balanceable system being in balance when the actual attack angle is that selected and when said craft is following a desired glide path; and means effective upon unbalance of said system to energize said motors for adjusting said throttles and said elevators until the actual attack angle becomes equal to that selected.

10. In apparatus of the class described, in combination: a powered aircraft; power control means and aerodynamic control means adjustable to cause movement of said craft at a selected attitude and airspeed within a range which may result in attack angles for the craft in excess of a predetermined magnitude; means responsive solely to actual attack angle; and means actuated by said responsive means only when the attack angle exceeds a predetermined magnitude to adjust both said control means so as to reduce said attack angle to said predetermined magnitude.

11. In apparatus of the class described, in combination: an aircraft having a power control member and a pitch attitude control surface; an attack angle sensing device; a vertical gyroscope; means normally connecting said gyroscope in controlling relation to said control surface; and means connecting said sensing device in controlling relation to said power control member and in overriding controlling relation to said control surface, so as to maintain a stabilized attitude and selected angle of attack.

12. Apparatus as in claim 11, including means effective whenever said attack angle exceeds a predetermined value, to cause corrective operation of said power control member and said pitch I control surface.

13. Attack angle control apparatus comprising, in combination: means responsive solely to actual attack angle; an attack angle selecting device; means giving first outputs whenever the actual attack angle is not that selected; means giving outputs which vary with throttle position and elevator position; means combining one of said first outputs and said elevator position output to comprise a first control signal; an elevator servomotor; means controlling the operation of said elevator servomotor in accordance with said first control signal; means combining the other of said first outputs and said throttle position output to comprise a second control signal; a throttle servomotor; and means controlling operation of said throttle servomotor in accordance with said second control signal.

14. Attack angle control apparatus comprising, in combination: means responsive solely to actual attack angle; an attack angle selecting device; means giving a first output whenever the actual attack angle is not that selected; a control sur face position responsive device; a pitch attitude selecting device; means giving a second output whenever said two last named devices are not in agreement; means combining said outputs to comprise a control signal; control surface servomotor means; and means controlling the operation of said servomotor means in accordance with said control signal.

15. In apparatus of the class described, in combination: means responsive solely to actual attack angle throughout a range of values extending on both sides of a predetermined value; stall prevention means actuated by said attack angle responsive means; and elevator control means actuated by said attack angle responsive means and by said stall prevention means.

16. In a device of the class described, in combination: control surface servomotor means; means giving a first output varying with deviation of actual attack angle from a selected value; means giving a second output whenever actual attack angle exceeds a selected value; means for giving a third output varying in accordance with deviation of a craft from a selected glide path; means combining said outputs to comprise a signal; and means actuating said servomotor means in accordance with said signal.

17. In an apparatus of the class described, in combination: an aircraft having a power control member and a pitch attitude control member; a device responsive solely to the attack angle of said aircraft throughout a range of values extending on both sides of a boundary value; and means actuated by said device, in response to values of said condition in excess of said bound: ary value, for actuating said members, in accordance with. the amount of said excess, in a direction to reduce said attack angle,

18. In an aircraft approach and landing system for maintaining an airplane on a glide path defined by electromagnetic radiation, receiver means responsive to said glide path, selector means responsive to said receiver means for establishing a requested angle of attack, detector means responsive to changes in the angle of attack of the airplane, means for maintaining said airplane at a substantially constant instantaneous attitude, regulating means for varying the power output from the power unit of the airplane, means responsive to action of said selector means and said detector means for controlling said regulating means whereby the angle of attack of said airplane is caused to vary to correspond with said requested angle of attack, and alarm means responsive to a predetermined critical position of said detector means for automatically increasing the power output from said power unit and for automatically changing said attitude when said airplane reaches a critical angle of attack.

19. In an aircraft approach and landing system for maintaining an airplane on a flight track along a glide path beam, glide path means comprising selector means responsive to vertical departures of the airplane from said glide path, detector means responsive to changes in the angle of attack of the airplane, regulating means for varying the power output from the power unit of the airplane, means for controlling the operation of said regulating means in response to said selector means and said detector means whereby said airplane is maintained on said glide path, automatic pilot means for controlling the attitude of said airplane, dive control means as an element of said automatic pilot means, and means responsive to said detector means for actuating said dive control means at a predetermined critical angle of attack of said airplane whereby the attitude angle of said airplane is reduced.

20. In apparatus of the class described, in combination: a throttle; a control surface; a motor for said throttle; a motor for said control surface; a balanceable system including a member freely pivoted about an axis forward of its center of resistance for movement into alignment with the relative wind, means actuated thereby to be responsive to actual attack angle, and attack angle selecting means, said system. being in balance when the actual attack angle is that select means connected to said system and motors and eiiective upon unbalance of said systern to energize said motors for adjusting said throttle and said control surface to an extent de termined by said unbalance.

21. In apparatus of the class described, in com bination: means for causing an aircraft to move at a constant altitude; a member freely pivoted about an axis forward of its center of resistance for movement into alignment with the relative wind, so as to respond positionally to the attack angle of the craft; and motor actuated means connected to said first named means and said member and controlled by said member for main taining a desired angle of attack while said altitude is maintained constant.

22. Apparatus of the class described comprising, in combination; a member freely pivoted about an forward of its center of resistance for movement into alignment with the relative wind; signal means connected to said member to give an output which varies with attack angle; power control means connected to said signal means for actuation in accordance therewith; stall prevention signal means connected to said first named signal means for adjustment in ac cordance with the signal therefrom; and elevator control means connected to said stall prevention signal means for actuation in accordance with the signal therefrom.

23. Attack angle control apparatus comprising, in combination: means responsive to actual attack angle including a member freely pivoted about an axis forward of its center of resistance for movement into alignment with the relative wind and a device connected to said member for adjustment in accordance with the position thereof to give a signal representative of the actual attack angle of the craft; means adjustable to give a signal representative of a selected value of attack angle; signal combining means interconnecting the above named means to give an output whenever the actual attack angle is not that selected; control surface servomotor means; and control means connected to said servomotor means and said signal combining means for controlling operation of said servomotor means in accordance with said output.

24. In control apparatus for an airborne craft having a propelling engine, in combination: means giving a first signal proportional to attack angle; means giving a second signal proportional to a variable factor affecting engine operation; means comparing said signals; and means adjusting the effective power of the engine whenever said signals are not in a desired relationship.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,367,839 Tarbox Feb. 8, 1921 1,760,740 Bramson May 2'7, 1930 1,832,159 Vanderlip Nov. 17, 1931 2,191,250 Fischel Feb. 20, 1940 2,343,288 Fink Mar. 7, 1944 2,553,983 Saxman, Jr May 22, 1951 

